1. Field of the Invention
This invention relates to a fault diagnosing apparatus for evapopurge systems, adapted to adsorb a transpiration gas in a fuel tank to a canister, and purge the canister of the adsorbed fuel and discharge the resultant fuel into a suction passage of an internal combustion engine.
2. Description of the Related Art
An internal combustion engine is usually provided with an evapopurge system for preventing a transpiration gas occurring in a fuel tank from being discharged to the atmosphere. The evapopurge system is adapted to adsorb a transpiration gas occurring in the fuel tank to the canister via a vapor passage communicating the fuel tank and canister with each other, and purge the canister of the adsorbed fuel and discharge the resultant fuel into a suction passage of an internal combustion engine via a purge passage communicating the canister and suction passage with each other.
When the vapor passage and purge passage are damaged from a certain cause in an internal combustion engine provided with such an evapopurge system, the transpiration gas is discharged from the damaged portion into the atmosphere. In order to eliminate such an inconvenience, a fault diagnosing apparatus for detecting damage to the vapor passage and purge passage is provided.
Such fault diagnosing apparatuses for evapopurge systems include, for example, the apparatus disclosed in Japanese Patent Laid-Open No. 159157/1994 (U.S. Pat. No. 5,425,344). In the fault diagnosing apparatus for evapopurge systems disclosed in this publication, an evapopassage including a fuel tank is depressurized by a negative pressure of a suction passage, and thereafter closed and repressurized, whereby the damage (leakage of a transpiration gas) to the evapopassage is detected on the basis of pressure variation occurring during this time.
However, in such a fault diagnosing apparatus for evapopurge systems, the hopping (which will hereinafter be referred to as sloshing) of a fuel in the fuel tank occurs due to the operating condition of a vehicle, and, during this time, an amount of a transpiration gas occurring from the fuel increases. In such a case, there is the possibility that the evapopurge system be diagnosed erroneously as being out of order. Namely, when the sloshing of the fuel causes the amount of the transpiration gas occurring therefrom to increase, the pressure in the fuel tank increases in accordance with the increase in the amount of transpiration gas when the depressurized evapopassage is closed and repressurized. Consequently, the regained pressure in the evapopassage becomes high in a short period of time. This causes the fault diagnosing system for evapopurge systems to judge that the evapopassage is damaged in spite of the fact that the evapopassage is not actually damaged (the leakage of the transpiration gas does not occur), and diagnose the evapopassage as being out of order.
The related art fault diagnosing apparatus for evapopurge systems disclosed in the above-mentioned publication is adapted to detect the occurrence of the sloshing of a fuel in the fuel tank, and interrupt a fault judgement operation when the sloshing of the fuel occurs.
A fault diagnosing apparatus for evapopurge systems which has been made with a view to solving similar problems is disclosed in U.S. Pat. No. 5,398,661 (EP0559854), the apparatus being adapted to interrupt a fault judgement operation when the fuel tank is in a filled-up condition since, in such a condition, there is the possibility that even a very low level of transpiration of the fuel causes the regaining of pressure to be attained in a short period of time; and carry out a fault judgement operation with the engine in an idling condition and at a vehicle speed of not higher than a predetermined threshold value.
In these related art fault diagnosing apparatuses for evapopurge systems described above, a fault judgement operation is interrupted when the sloshing of a fuel occurs or when the fuel tank is in a filled-up condition, so that a fault of an evapopurge system is not erroneously diagnosed.
However, since the fuel tank is vibrated during the travel of a vehicle, the sloshing of a fuel more or less occurs. Consequently, in the apparatus of Japanese Patent Laid-Open No. 159157/1994, in which a fault judgement operation is interrupted when the sloshing of a fuel occurs, the opportunity of practicing a fault diagnosing operation for the evapopurge system is limited, so that a sufficient fault diagnosing operation cannot be carried out. In the apparatus of U.S. Pat. No. 5,398,661, in which a fault judgement operation is also carried out when the fuel tank is not in a filled-up condition with the engine and a vehicle speed in an idling condition and at a level not higher than a predetermined level respectively. Even in such an operating condition, the fault judgement operation receives influence of the occurrence of the sloshing of the fuel, and an erroneous judgement cannot be prevented.
The present invention has been made in view of the above-mentioned circumstances, and provides a fault diagnosing apparatus for evapopurge systems, capable of solving these problems, preventing the sloshing of a fuel from causing an erroneous judgement that an evapopurge system is out of order to be given, and reliably determining a fault of the evapopurge system no matter what the operating condition of the engine is.
According to an aspect of the present invention, the fault diagnosing apparatus for evapopurge systems includes a device for detecting a pressure in an evapopassage inclusive of a fuel tank, a depressurization device adapted to close a first valve, which is provided in an atmosphere-opened port of a canister, and depressurize the interior of the evapopassage by a negative pressure occurring in the interior of a suction passage, a repressurization device adapted to close a second valve, which is provided in a purge passage, after the depressurization device is operated, to repressurize the interior of the evapopassage, and a fault judgement device adapted to permit a judgement, which is based on an output from the pressure detecting device, that the evapopurge system is abnormal to be given on condition that the depressurization device and repressurization device are operated plural times.
When the depressurization and repressurization of the interior of the evapopassage are carried out plural times, the air in the evapopassage is discharged, and the evapopassage is filled with a transpiration gas, i.e., put in a saturated state, so that pressure variation ascribed to the sloshing of the fuel does not substantially occur. When a fault diagnosing operation for the evapopurge system is carried out in this condition on the basis of an output from the pressure detecting device, a fault can be determined accurately.
According to another aspect of the present invention, the fault diagnosing apparatus includes a device for detecting an amount of a fuel remaining in a fuel tank, and a device for setting the number of times of execution of operations of a depressurization device and a repressurization device on the basis of an output from the amount of remaining fuel detecting device. A generation rate of the transpiration gas differs with the amount of the fuel remaining in the fuel tank. Accordingly, when the number of times of execution of the operations of the depressurization and repressurization devices is set on the basis of the amount of the remaining fuel, a fault of the evapopurge system can be determined accurately.
In the fault diagnosing apparatus for evapopurge systems, in which the number of times of execution of operations of depressurization and repressurization devices is set on the basis of an amount of a remaining fuel, the increasing of the number of times of execution of the depressurization and repressurization of the interior of an evapopassage in accordance with a decrease in the amount of the remaining fuel enables a fault to be determined more accurately.
Operating the fault judgement device when the amount of the remaining fuel determined by the amount of remaining fuel detecting device is larger than 40% of the capacity of the fuel tank reduces the fault diagnosis continuation time, and is therefore preferable. It is also preferable to provide a fuel temperature detecting device, and change the number, which is set by the number of operation setting device, of the execution of depressurization and repressurization operations on the basis of an output from the fuel temperature detecting device. This enables the numbers of the execution of the depressurization and repressurization operations to be set properly, and the fault diagnosis continuation time to be reduced.
According to still another aspect of the present invention, the fault diagnosing apparatus includes a device for detecting an amount of a fuel remaining in a fuel tank, and a fault judgement device, the fault judgement device including a member for setting reference number of times of execution of operations of depressurization and repressurization devices on the basis of an output from the amount of remaining fuel detecting device, and a reference value setting member for setting a reference repressurization value on the basis of an output from the amount of remaining fuel detecting device, the fault judgement device being preferably adapted to judge that an evapopurge system is normal when the number of times of execution of the operations of the depressurization and repressurization devices is not smaller than one and not larger than the reference number set by the number of times of operations setting member with a regained pressure in an evapopassage detected by a pressure detecting device becoming not higher than a reference regained pressure value set by the reference value setting member; and judge that the evapopurge system is abnormal when the number of times of execution of the operations of the depressurization and repressurization devices exceeds the reference number of times set by the number of times of operations setting member with regained pressure in the evapopassage detected by the pressure detecting device every time the depressurization and repressurization operations are executed exceeding a reference regained pressure value set by the reference value setting member. Since the normality of the evapopurge system can be determined speedily, and since the determination of the abnormality thereof can be done accurately, the reduction of total fault diagnosis continuation time can be attained.